The present invention concerns a polyol combination, the preparation of polyurethane foam from this polyol combination, the foam itself and shaped articles comprising the foam.
The present invention concerns a polyol combination which is very suitable for preparing shaped, flexible polyurethane articles by moulding techniques.
Moulding techniques for preparing shaped polyurethane articles are well known in the art. These techniques could be divided into to main groups: hot cure moulding and cold cure moulding techniques. The present invention particularly concerns a polyol combination which can suitably be applied in cold cure moulding, although application thereof in hot cure moulding would also be possible.
Typically, hot cure moulding techniques involve pouring a foaming mixture into a mould, after which a significant amount of external heat is applied to the mould, for instance by placing the mould in an oven at 180-300xc2x0 C., in order to effect sufficient surface curing of the foam in the mould so that it can be removed from the mould quickly. Typical mould temperatures when pouring the reaction mixture into the mould are from 25 to 45xc2x0 C. Cold cure moulding techniques, also sometimes referred to as high resilience moulding techniques, require much less external heat to be applied to the mould. This is achieved by using more reactive polyol molecules, so that the chemical reactions proceed faster and less overall cure energy is needed. Typical cold cure moulding temperatures range from 40 to 70xc2x0 C.
The polyol combination of the present invention is particularly useful to prepare tailor made polyurethane articles to be used for sound deadening purposes in cars and trucks. Namely, it has already been and replace it with recognized for a long time that the interior noise level of a vehicle has comfort and safety implications for its driver. As a result hereof, car and truck manufacturers are continuously looking for means to further reduce the noise level in the interior parts of cars and trucks. A major component of the noise inside a car is the airborne noise originating from the engine compartment. This can be readily reduced by installing a carpet having a backing of sound deadening material, such as e.g. a polyurethane foam, which carpet covers the metal partition between the engine and driver/passenger compartment.
For a polyurethane foam to be suitable as sound deadening material it should on the one hand have sufficient density to absorb the sound waves causing the noise. At this moment the lowest achievable overall densities of commercially applied sound deadening foams are around 50-55 kg/m3. Densities of this order of magnitude are considered necessary to attain sufficient sound deadening properties. On the other hand there is a constant effort in the sound deadening market to reduce the foam density, whilst still maintaining the requirements as regards foam processing and sound absorption. One of the objects underlying the present invention, therefore, is to provide a polyol combination which enables the production of sound deadening polyurethane sheets, whereby the processability of the foam formulation containing the polyol combination is very good, whilst the polyurethane sheet prepared has excellent sound deadening properties at very low densities.
This object has been achieved by a polyol combination comprising two polyol components with distinct properties and essentially no stably dispersed polymer particles, i.e. the polyol combination of the present invention is free of any polymer polyol component.